This invention relates generally to an impact printer of the type having a character drum with a plurality of columns of characters around the periphery thereof and more particularly to an impact printer having a mask through which a hammer strikes selected characters on the drum. The mask presents a bar between each column on the drum and is positioned between the drum and a print media, for example, paper. In the conventional manner, the paper is positioned between the mask and the hammer which strikes against the character drum through the paper and the opening in the mask. Conventionally, the mask is fixed to the printer frame by means of screws or other similar fasteners. When the diameter of the character drum changes due to changes in ambient temperature, the distance between the characters on the drum and the mask changes such that the spacing becomes more or less whereby the paper may become marred or dirty during printing and the characters may be too light or too dark. In the prior art, masks have been made using two kinds of metal in a bimetal arrangement so that the mask bends with changes in the ambient temperature. In this way the distance between the characters and the mask is varied. In such a construction using bimetals the problems of non-uniform quality and marring of the print media are resolved to a degree but the cost is substantially increased because of the use of bimetals. Accuracy in obtaining the desired results is low because the mask has been supported on one side.
What is needed is a small sized impact printer having a mask which prevents marring of the print media and assures uniform quality of print by automatic adjustments to compensate for variations in ambient temperature.